Wearing her wedding ring as she posed for photos, "she was all smiles," a friend of the actress tells PEOPLE of her appearance at the event, which honored screen icon Jane Fonda. "She was with Eva and called her 'my date,' and randomly said she was doing 'good.' "

But the next day Academy Award nominee Griffith filed for divorce from her husband of 18 years, surprising many, including those who know her well.

"They've been down this road before but I never thought it would actually happen," the friend says. "There's so much love there."

The couple, who met in 1995 while working on the film Too Much, had weathered problems in the past, including a rocky patch when Griffith (who has his name tattooed in a heart on her right arm) checked into rehab for a third time in 2009.

"We have had as many problems as anybody. We've never hidden it," Banderas, 53, told AARP The Magazine.

But rumors of marital trouble surfaced again in 2012 after Banderas was spotted getting cozy with two different women.

While Griffith, 56, is seeking spousal support from Banderas and physical custody of their daughter, Stella, who turns 18 in September, the friend says it's unlikely their split will turn into an ugly Hollywood divorce.

"I could never see it getting nasty," the friend says. "It's just not them."

Adds a second source: "They were so good together. I hate to see marriages end, especially ones that are as solid as theirs for so many years. I'm sad to see it ending."